Is Lindsey Halligan a “stalking horse” for President Donald Trump’s revenge against James Comey? The answer could doom the prosecution against the former FBI director that Trump demanded.

The term “stalking horse” has come up in previous cases in which defendants have claimed vindictive prosecution, as Comey does in a pending motion to dismiss his charges. To establish that hard-to-win claim, defendants must show 1) that the prosecutor acted with genuine animus, and 2) that the defendant wouldn’t have been charged without that animus.

The Department of Justice wants to limit the analysis to Halligan’s motives, while Comey’s team says the president’s ill will against the defendant should be imputed to the Trump-installed prosecutor, who was previously the president’s personal lawyer, lacked prior prosecutorial experience and secured the indictment over the objection of career prosecutors.

In support of their position that imputing Trump’s animus to Halligan is appropriate, Comey’s lawyers cite case law for the proposition that one way to prove ill intent is by showing that the prosecutor “was prevailed upon to bring the charges by another with animus such that the prosecutor could be considered a ‘stalking horse.’” The DOJ argues that the federal appellate circuit covering Virginia, where Comey was indicted, has never endorsed that imputed-animus theory, and the prosecution denies that Trump has displayed sufficient animus in any event.

Replying to the DOJ’s argument on Monday, Comey’s lawyers quote from the Supreme Court’s Trump immunity ruling, writing that tracing the president’s motives to Halligan “is particularly warranted because the President has ‘exclusive authority over the investigative and prosecutorial functions of the Justice Department and its officials.’” They go on to note that Trump “has exercised an unprecedented and extraordinary degree of control over the DOJ, installing his personal allies to key positions and inserting himself into prosecutorial decisions that, in previous Administrations, would have been left to the DOJ’s independent judgment.”